1. Field of the Invention
This invention relates generally to a photographic exposure control system having independent ambient and artificial scene illumination control modes, and more particularly to a photographic exposure control system embodying scanning type shutter blades having two separate sets of photocell sweep secondary apertures, each set of which controls the admittance of scene light to a photoresponsive element in correspondence with the scene light admitted to the film plane during either an ambient or artificially scene lighted mode of operation.
2. Description of the Prior Art
Recently, cameras embodying "scanning type" shutter blade arrangements have been used in conjunction with fixed focus objective lenses to provide a camera which is simple to operate. One camera of this type is currently marketed by the Polaroid Corporation under the trade name "One Step". This camera utilizes film units of the self-processable type which are automatically processed and ejected from the camera by way of a motorized drive mechanism. Thus, the photographer need only depress a single button to effect both the exposure and processing of the film units.
One exposure control system which is particularly suited for use in such cameras is described in a copending Application Ser. No. 801,477 entitled "Scanning Shutter Blade Arrangement With Ambient And Flash Ranges" by B. K. Johnson et al. filed May 31, 1977 in common assignment herewith and discloses a means by which the scene light admitted to a photoresponsive element may be controlled in a different manner for the natural or ambient scene lighted mode of operation than for the artificial scene lighted mode of operation. This is accomplished by providing the scanning shutter blade elements with photocell sweep secondary apertures to control the admittance of scene light to the photoresponsive element in correspondence with the admittance of scene light to the film plane in a manner as is already known in the art. In the natural or ambient scene lighted mode of operation, the exposure control limits the size to which the effective primary aperture and the effective photocell sweep secondary aperture can progressively open to a first range. During the artificial scene lighted mode of operation, the source of artificial illumination is fired at a point in time coinciding with the shutter blade elements reaching their maximum effective aperture defining positions within the first range. Subsequent to firing the flash, the shutter blade elements continue to open to define a second range of progressively increasing sized apertures beyond the first range of the ambient scene lighted mode of operation. Thus, the photocell sweep secondary apertures may be further configured to control the scene light admitted to the photoresponsive element in its second range of progressively increasing sized apertures in a manner which is especially suited for the artificially scene lighted mode of operation.
Although the photocell sweep secondary apertures may be configured to provide effective control in either the ambient scene lighted mode of operation through its first range of progressively increasing sized apertures or in the artificially scene lighted mode of operation through its second range of increasing sized apertures, there will be incurred a slight loss in the depth of field for the artificially scene lighted mode of operation since the second range of effective apertures are larger than the first range of effective apertures utilized during the ambient scene lighted mode of operation.
Thus, it is a primary object of this invention to provide a photographic exposure control system wherein the exposure may be controlled independently in either the ambient scene lighted mode of operation or the artificial scene lighted mode of operation without changing the range of effective apertures utilized between modes of operation.
It is also an object of this invention to provide a photographic exposure control system wherein the artificial scene lighted mode of operation may be controlled in a manner different from the ambient scene lighted mode of operation while still using only a single photocell and without changing the depth of field between the two modes of operation.
Other objects of the invention will be part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.